I have some problems with some clients using Internet Explorer 7 to access an internal web application.
The problem:
Sometimes, IE7 on the client fails to load part of web pages or some images on that page. It is not systematic (i.e. the same page sometimes loads correctly and sometimes not, and the page with the problem varies every time) and it appears to be random, but it happens quite enough frequently to have those users complain a lot.

What I have excluded:
Other clients on the same network, accessing the same web application on the same server, doesn't have the problem, so it doesn't appear to be caused by the server, the application or the network.
The malfunctioning clients also have some similar problems when browsing the internet, so it doesn't appear to be caused by the internal web app.
Other clients also have IE7 and no problems, so it doesn't appear to be connected with the particular version of IE.

What I tried:
I applied Windows XP SP3 to those PC, and all patches from Microsoft Update, with no result.
I have scanned the PC for viruses, and found none active.
I have disabled the antivirus, with no result (and other clients with the same antivirus have no problems).
Unfortunately, I can't try with different browsers, because the web app is designed to run only on IE.

What I suppose:
I know that those PCs have been infected with Conficker Worm some weeks ago, so it could have left some corrupted files or registry entry. But I don't know what to search for, or how to repair it.
IF the problem is confirmed to be caused by IE, would the upgrade to IE8 solve the problem? Would a complete uninstall and reinstall of IE7 solve it?

I will appreciate any help you can offer, especially if you have experienced the same problem.

3 Answers
3

A)
It's a bit tricky, but you might need to find the files that conflicker modified/infected and make sure there isn't a config file (or registry) somewhere in the computer(s) blocking access to the addresses those websites are trying to get to. A great tool for finding modified (unusually configured registry settings, DLLs and other windows system files) is hijackthis from Trend Micro.

You might want to do a view source on the webpage and see what addresses aren't loading and do systematic troubleshooting from that perspective

B) Ultimately, I would say "re-install everything!" but I don't know your situation. I'm somewhat neurotic about viruses so I would re-install if I could.

Thank you. I'll try the tool tomorrow. I'm not a fan of "re-install everything", because it's going to take a lot of time, and it wouldn't give me a solution for the others PCs which have, or will have, the same problem.
–
Andrea BertaniMay 4 '09 at 21:45

Thanks to all for the suggestions.
However, Hijackthis didn't show anything strange, and uninstalling IE7 has turned out to be a bad idea, since I wasn't able to reinstall it.
Microsoft says that if you have SP3 installed you can't uninstall IE7. It's wrong. You can uninstall it, but you can't reinstall it again!
However, I was able to install IE8, but the problem was showing up even more frequently!

I happened to fix it by deleting webproxy.exe, which is part of our Panda Security antivirus solution. I'm not sure if the antivirus is working well now, but the problem seems vanished.
I still don't understand why similar PCs with the same SP3, IE7 and Panda antivirus are not showing any malfunctioning...

Hmm... well, good job finding that. Though from googling "Panda security" solutions you can find that it is a common problem for people (webproxy.exe). I'm not seeing very good reviews about their 'solution'.
–
l0c0b0xMay 7 '09 at 16:53